Slide rail device for vehicle seat

ABSTRACT

A slide rail device which includes a lower rail, an upper rail which is freely slidably engaged with the lower rail, and balls which are installed between the lower and upper rails. The lower rail includes a lower-rail bottom wall, a pair of lower-rail side walls, a pair of lower-rail upper wails, a pair of lower-rail lower-ball contact R-portions, and a pair of lower-rail upper-ball contact R-portions. The upper rail includes an upper-rail top wall, a pair of upper-rail side walls, and a pair of upper-rail ball-bearing walls. Each upper-rail ball-bearing wall includes an upper-rail lower-ball contact portion and an upper-rail upper-ball contact portion. A radius of curvature of the lower-rail lower-ball contact R-portion of the lower rail is greater than that of the lower ball, and a radius of curvature of the lower-rail upper-ball contact R-portion of the lower rail is greater than that of the upper ball.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a slide rail device for

making an adjustment to the position of a vehicle seat, in theforward/rearward direction.

2. Description of Related Art

A typical slide rail device (slide rail assembly) is configured of alower rail that, is fixed to a vehicle floor, an upper rail that isfixed to a vehicle seat and engaged with the lower rail to be freelyslidable thereon, and balls (steel balls) for reducing frictionalresistance that are installed between the upper rail and the lower rail.The upper rail and the lower rail are each made of a metallic material(usually an iron-based material) having a uniform cross section. Such aslide rail device is disclosed, in Japanese Patent Publication No4,230,945.

In this known slide rail device, application of a force on the upperrail and the lower raid, therebetween that is produced by the weight ofsomeone (a driver or a passenger) sitting in the vehicle seat causesrelatively large forces that exert, on the rails at points of contactwith the balls. As a consequence; sometimes indentations are made on therails via the balls. Since such indentations obviously deteriorate thereliability of the balls, it Is desirable that the rails be formed intoa shape preventing such indentations from being made on the rails asmuch as possible. For this reason, the radius of the balls has been setto be identical to the radius of curvature of the ball contact portionsof each rail in conventional slide rail devices. Namely, if the radiusof the balls is identical to the radius of curvature of the ball contactportions of each rail, the surface pressure exerted on the rails is at ageometric minimum, so that the possibility of indentations being made onthe rails via the balls is low. However, the inventor of the presentinvention has found that, if the radius of the balls is made to beidentical in design to the radius of curvature of the ball contactportions of each rail, the rollability of the balls sometimesdeteriorates regardless of the presence

or absence of indentations on the rails (aside from the problem ofindentations), to thereby make the sliding operation of the upper railwith respect to the lower rail unstable.

SUMMARY OF THE INVENTION

As a result of having pursued the cause of the lack of stability of thesliding operation of the slide rail, device, the inventor of thepresent, invention has completed the present invention after coming tothe conclusion that if the radius of the balls is made to be identicalto the radius of curvature of the ball contact portion of each rail,there is a possibility of a combination of a ball and a rail beingunintentionally produced in which the radius of curvature of the ballcontact portion of the rail is smaller than the radius of the balls dueto manufacturing error, thus causing the ball and the rail to be incontact with each other at two points to thereby deteriorate thereliability of the balls. The balls (steel balls) are extremely high indimensional accuracy and hardness, as is known in the art, so that thereis little possibility of an error in the dimensional accuracy of theballs affecting the reliability thereof. The length (angle) of thecircular arc in each ball contact R-portion of the lower rail is usuallygreater than that of the upper rail, so that the shapes of the basilcontact R-portions of the lower rail greatly affect the reliability ofthe balls.

According to an aspect of the present invention, a slide rail device isprovided, which includes a lower rail having a uniform cross section, anupper rail having a uniform cross section which is freely slidablyengaged with the lower rail, and balls which are installed between thelower rail and the upper rail, The lower rail includes a lower-railbottom wall; a pair of lower-rail side walls which extend upward fromboth ends of the lower-rail bottom wall, with respect to a lateraldirection, respectively; a pair of lower-rail upper walls which extendtoward a center of the lower rail in the lateral direction from upperends of the pair of lower-rail side walls, respectively; a pair oflower-rail lower-ball contact R-portions via which the pair oflower-rail side walls are connected to the lower-rail bottom wall,respectively; and a pair of lower-rail upper-ball contact R-portions viawhich the pair of lower-rail upper wails are connected to the pair oflower-rail side walls, respectively. The upper rail includes anupper-rail top wall; a pair of upper-rail side walls which arecontinuous with the upper-rail top wall and extend downward between thepair of lower-rail upper walls into the lower rail from both ends of theupper-rail top wall, with respect to a lateral direction, respectively;and a pair of upper-rail ball-bearing walls which extend outwardlyupwards from lower ends of the pair of upper-rail side walls,respectively. Each of the pair of upper-rail ball-bearing wails includesan upper-rail lower-ball contact portion which is formed to face anadjacent lower-rail lower-ball contact R-portion of the pair oflower-rail lower-ball contact R-portions of the lower rail, and anupper-rail upper-ball contact portion which is formed to face anadjacent lower-rail upper-ball contact R-portion of the pair oflower-rail upper-ball contact R-portions of the lower rail. The ballsinclude a pair of upper balls which are installed between the pair oflower-rail upper-ball contact R-portions of the lower rail and theupper-rail upper-ball contact portions of the pair of upper-railball-bearing wails of the upper rail, respectively; and a pair of lowerballs which are installed between the pair of lower-rail lower-ballcontact R-portions of the lower rail and the upper-rail lower-ballcontact portions of the pair of upper-rail ball-bearing wails of theupper rail, respectively. A radius of curvature of the lower-raillower-ball contact E-portion of the lower rail is

greater than a radius of the lower ball, and a radius of curvature ofthe lower-rail upper-ball contact R-portion of the lower rail is greaterthan a radius of the upper ball.

Note that the term “R-portion” denotes a portion of the lower or upperrail which is formed into a circular arc shape with a specific:curvature in cross section. This curvature can be circular orelliptical. In addition, the term “lateral” denotes a lateral directionin a vehicle widthwise direction, and the term “outward” denotes anoutward direction from, a cross sectional center of the rail,

Although both the upper-rail upper-ball contact portion and theupper-rail lower-ball contact portion of each of the pair of upper-railball-bearing wails can be formed as flat surfaces, it is desirable thatat least the upper-rail upper-ball contact portion of each of the pairof upper-rail ball-bearing walls of the upper rail be formed as anupper-rail upper-ball contact R-portion that is formed into a circulararc shape with a specific curvature in cross section. This is becausethe ratio between the force that acts on the pair of upper-railball-bearing walls via the upper balls and the associated reaction forcecaused by deformation, of the rails (the pair of upper-rail ball-bearingwalls) is greater than the ratio between the force that acts on the pairof upper-rail ball-bearing walls via the lower balls and the associatedreaction force caused by deformation of the rails (the pair ofupper-rail ball-bearing walls), and accordingly, it is desirable thatthe upper-rail upper-ball contact portion of each upper-railball-bearing wall be formed as the aforementioned upper-rail upper-ballcontact R-portion that is smaller in surface pressure than a fiatsurface. In addition, the radius of curvature of the upper-railupper-ball contact R-portion is desirably set to be greater than theradius of the upper ball due to the same reason as that of the radius ofcurvature of the lower-rail lower-ball contact R-portion being greaterthan the radius of the lower ball.

It is desirable that the upper-rail lower-ball contact portion of eachupper-rail ball-bearing wall of the upper rail be also formed as anupper-rail lower-ball contact R-portion (that is formed into a circulararc shape with a specific curvature in cross section) rather than a fiatsurface. In this case, it is desirable that the radius of curvature ofthe upper-rail lower-ball contact R-portion be also set to be greaterthan the radius of the lower ball.

It is desirable for the following conditions to be satisfied;

R1≧.1 and R2≧1.1r2,

more desirably R1≧1.2r1 and R2≧1.2r2,

wherein r1 designates the radius of the lower ball, r2 designates theradius of the upper ball, R1 designates the radius of curvature of thelower-rail lower-ball contact R-portion, and R2 designates the radius ofcurvature of the lower-rail upper-ball contact R-portion, Consideringdimensional errors of the rails in manufacturing, if R1 and R2 aresmaller than 1.11 r and 1.11 r 2, respectively, it has been confirmedthat the reliability of the balls deteriorates (a combination of a balland a rail in which the radius of curvature of the ball contact portionof the rail is smaller than the radius of the ball is unintentionallyproduced), though the surface pressure exerted on the rails is reduced.

On the other hand, the upper limit of the radius of curvature (R1 or R2)of each ball contact R-portion is determined so that the surfacepressure at the ball contact. R-portion, with which the balls are incontact, becomes equal to or smaller than an allowable surface pressurein consideration of the material of the rails.

In the slide rail device according to the present invention, it isconceivable that each of inner surfaces of the two connecting cornersbetween the upper wall of the upper rail and the pair of upper-rail sidewalls of the upper rail, respectively, serves as an assumed deformationrotational center when the upper rail is resiliently deformed upon anormal load being applied thereto. In an embodiment of the slide raildevice according to the present invention, each inner surface of twoconnecting corners between the upper-rail top wall of the upper rail andthe pair of upper-rail side walls of the upper rail serves as an assumeddeformation rotational center when the upper rail is resilientlydeformed upon a normal load being applied thereto, and a cross sectionalshape of the upper rail is determined so as to define an outwardcrossing angle between a line segment, which connects the assumeddeformation rotational center and a center of associated one of the pairof lower balls and a line segment which is tangent to both theassociated, one of the pair of lower balls and the upper-rail,lower-ball contact R-portion at an angle in a range from 80 degrees toless than 30 degrees, desirably in the range from 80 to 88 degrees.

By setting the outward crossing angle in this manner, the pair ofupper-rail side walls can be securely made to be resiliently deformableinwardly (i.e., in directions toward each other) via the lower balls. Ithas been confirmed that deformation of the pair of upper-rail side wallsoutwardly in opposite directions away from each other may deterioratethe slidability of the slide rail device.

If the aforementioned outward crossing angle is set at an angle of 90degrees, the load carrying capacity of the upper rail 30 becomes maximumin theory. However, if the outward crossing angle is set at an angle of90 degrees, a combination of a ball and a rail in which the outward,crossing angle exceeds 90 degrees may be unintentionally produced due tomanufacturing error, which may cause the pair of upper-rail side wallsto be deformed outwardly in opposite directions away from each other.

According to the present invention, the radius of curvature of each ballcontact R-portion of at least the lower rail is set to be greater thanthe radius of the associated balls, which makes it possible to obtain aslide rail device in which the indentation prevention performance andthe reliability of the ball are well-balanced.

It is desirable for the lower rail to include a pair of lower-rail innerside wails which are positioned between the

pair of lower-rail side wails and extend downward from inner ends of thepair of lower-rail upper walls, respectively.

It is desirable for each of the pair of upper-rail ball-bearing wails toinclude a vertical connecting wall via which the upper-rail lower-ballcontact portion and the upper-rail upper-ball contact portion areconnected.

The present disclosure relates to subject matter contained in JapanesePatent Application No. 2010-277512 (filed on Dec. 13, 2010) which isexpressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be discussed below in detail with referenceto the accompanying drawings, in which;

FIG. 1 is a longitudinal sectional view of an embodiment of a slide raildevice according to the present invention;

FIG. 2 is a sectional view of part of the upper rail shown in FIG. 1,showing the detailed shape thereof; and

FIG. 3 is a graph showing experimental data on the relationship betweenthe contact-surface pressure and the radius of curvature (R) of a ballcontact R-portion divided by the radius (r) of the ball.

DESCRIPTION OF THE EMBODIMENT

FIG. 1 shows an embodiment of a slide rail device 10 according to thepresent invention. The slide rail device 10 is provided with a lowerrail 20 and an upper rail 30 which are fixed to a vehicle floor (notshown) and a vehicle seat (not shown), respectively, and is providedbetween the lower rail 20 and the upper rail 30 that are engaged witheach other to be relatively slidable, with two types of steel balls,i.e., lower balls 40 and upper balls 50, which are installed between thelower rail 20 and the upper rail 30. The slide rail device isbilaterally symmetrical in shape in a cross section taken along a planenormal to the extension direction (lengthwise direction) of the rails 20and 30. The lower balls 40 are greater in diameter than the upper balls50. As known in the art, two of the slide rail devices 10 are used as apair (left and right slide rail devices) in a state of being fixed to avehicle, and a lock mechanism and other components are installed to thispair of slide rail devices. However, since the main concept of thepresent embodiment is centered, around the uniform cross-sectionalshapes of the lower rail 20 and the upper rail 30, only such crosssectional shapes of the lower rail 20 and the upper rail 30 will bediscussed in the following descriptions. Additionally, in the followingdescriptions, the terms “lateral” denote a lateral direction in avehicle widthwise direction, respectively, the term “outward” denotes anoutward direction from a cross sectional center of the lower rail 20 orthe upper rail 30, and the term “R-portion” denotes a portion of thelower rail 20 or the upper rail 30 which is formed into a circular arcshape with a specific curvature in cross section.

The lower rail 20 is provided with a lower-rail bottom wall 21, a pairof lower-rail outer side walls 22, a pair of lower-rail, upper wails 23and a pair of lower-rail inner side wails 24, The horizontal, lower-railbottom wall 21 is fixed to a vehicle floor; the pair of lower-rail outerside walls 22 extend upward from both ends (sides) of the lower-railbottom wall 21, with respect to the lateral direction, respectively; thepair of lower-rail upper walls 23 extend in the lateral direction towardthe longitudinal center of the lower rail 20 from upper ends of the pairof lower-rail outer side wails 22, respectively; and the pair oflower-rail inner side walls 24 extend downward front inner ends of thepair of lower-rail upper walls 23, respectively, and are positionedbetween the pair of lower-rail outer side walls 22.

The lower-rail bottom wall 21 and the pair of lower-rail outer sidewalls 22 are connected via a pair of lower-rail lower-ball contactR-portions 25, respectively, and the pair of lower-rail outer side wails22 and the pair of lower-rail upper wails 23 are connected via a pair oflower-rail upper-ball contact R-portions 26, respectively.

The upper rail 30 is provided with an upper-rail top wall 31, a pair ofupper-rail side wails 32 and a pair of upper-rail ball-bearing wails 33,The horizontal upper-rail top wall 31 is fixed to a vehicle seat. Thepair of upper-rail side walls 32 are continuous with the upper-rail topwall 31 and extend downward between the pair of lower-rail inner sidewalls 24 into the lower rail 20 from both ends (sides) of the upper-railtop wall 31, with respect to the lateral direction, respectively. Thepair of upper-rail ball-bearing walls 33 extend outwardly upwards,toward the pair of lower-rail upper walls 23, from

the lower ends of the pair of upper-rail side walls 32, respectively.

Each, upper-rail ball-bearing wall 33 is provided at a lower partthereof with an upper-rail lower-ball contact R-portion 34 which isformed to face the adjacent lower-rail lower-ball contact R-portion 25of the lower rail 20, and is provided above the upper-rail lower-ballcontact R-portion 34 with an upper-rail upper-ball contact R-portion 35which is formed to face the adjacent lower-rail upper-ball contactR-portion 26 of the lower rail 20, Each upper-rail ball-bearing wall 33is further provided between the upper-rail lower-ball contact R-portion34 and the upper-rail upper-ball contact R-portion 35 with a vertical,connecting wall 36 via which the upper-rail lower-ball contact R-portion34 and the upper-rail upper-ball contact R-portion 35 are connected.

The upper-rail, lower-ball contact R-portion 34 and the upper-rail,upper-ball contact R-portion 35 of each upper-rail ball-bearing wall 33each have a curvature so as to hold (insert) the lower balls 40 betweenthe upper-rail lower-ball contact R-portion 34 and the adjacentlower-rail lower-ball contact

R-portion 25 and to hold (insert) the upper balls 50 between theupper-rail upper-ball contact R-portion 35 and the adjacent lower-railupper-ball contact R-portion 26, However, the upper-rail lower-ballcontact R-portion 34 and the upper-rail upper-ball contact R-portion 35of each upper-rail ball-bearing wall 33 are smaller in area (angle) atwhich a curvature is formed than the adjacent lower-rail lower-ballcontact R-portion 25 and the adjacent lower-rail upper-ball contactR-portion 26, respectively. Each adjacent lower-rail lower-ball contactR-portion 25 and each adjacent lower-rail upper-ball contact R-portion26 are formed to extend, by an angle of 90 degrees, whereas the curvedarea (angle) of the upper-rail lower-ball contact R-portion 34 of eachupper-rail ball-bearing wall 33 in particular is small, (can be reduced), thus capable of being replaced by a flat surface (flat surface area).

The radius of curvature R1 of the lower-rail lower-ball contactR-portions 25 and the radius of curvature R1′ of the upper-raillower-ball contact R-portions 34 are each defined greater than theradius r1 of the lower balls 40. Likewise, the radius of curvature R2 ofthe lower-rail upper-ball contact

R-portions 26 and the radius of curvature R2′ of the upper-railupper-ball contact R-portions 35 are each defined greater than theradius r2 of the upper balls 50. The radius of curvature R1 and theradius of curvature R1′ can be mutually identical or slightly differentfrom each other. Likewise, the radius of curvature R2 and the radius ofcurvature R2′ can be mutually identical or slightly different from eachother.

FIG. 3 is a graph showing experimental data indicating variations of thecontact-surface pressure at a ball contact R-portion (25, 26, 34 or 35)when the ratio between the radius r (r1 or r2) of the lower balls 40 orthe upper balls 50 and the radius of curvature R (R1, R2, R1′ or R2′) ofthe ball contact R-portion (25, 26, 34 or 35) is changed. As can beunderstood from the graph of FIG. 3, a boundary at which thecontact-surface pressure drastically changes exists (is defined) betweena point where the value R/r (the radius of curvature R divided by theradius r) is equal to 1.1 and a point where the value R/r is equal to1.2. Considering this fact and variations in radius of curvature of theball contact E-portions of the lower rail 20 and the upper rail 30 dueto manufacturing error, reliable reliability of the lower balls 40 andthe upper balls 50 can be ensured regardless of variations in radius ofcurvature R of the ball contact R-portion 25, 26, 34 or 35, by settingthe radius of curvature R so as to be equal to or greater thanapproximately 1.1 times of the radius r (i.e., R 1.1 r); more desirablyequal to or greater than approximately 1.2 times of the radius r(i.e.,≧R 1.2 r), On the other hand, the upper limit of the radius ofcurvature R (R1 and R2) of each ball contact R-portion (25 and 26) isset so that the surface pressure at the ball contact R-portion, withwhich the balls (40 or 50) are in contact, becomes equal to or smallerthan an allowable surface pressure in consideration of the material ofthe rails.

In addition to each lower-rail lower-ball contact R-portion 25 and eachlower-rail upper-ball contact R-portion 25, each upper-rail lower-ballcontact R-portion 34 and each upper-rail upper-ball contact R-portion 35are also each formed as an R-portion in the above illustratedembodiment; however, each upper-rail lower-ball contact R-portion 34 inparticular among each upper-rail lower-ball contact R-portion 34 andeach upper-rail upper-ball contact R-portion 35 can be made as a flatportion. On the other hand, it is desirable that each upper-railupper-ball contact R-portion 35 be formed as an R-portion which issmaller in surface pressure than a fiat surface like the above describedembodiment because each upper-rail upper-ball contact R-portion 35 playsa role in providing flexibility to the associated upper-railball-bearing wall 33 via the associated lower ball 40.

FIG. 2 is a diagram for illustrating a desirable shape of the upper rail30 in its free state. In each of left and right halves of the upper rail30 (only a left half of the upper rail 30 is shown in FIG. 2), an innersurface of the connecting corner between the upper wall 31 and theupper-rail side wall 32 becomes an assumed deformation rotational centerX when the upper rail 30 is resiliently deformed upon a normal loadbeing applied thereto. The cross sectional, shape of the upper rail inits free state is determined so as to define an outward crossing anglebetween a line segment Y, which connects the assumed deformationrotational center X and the center of the associated lower ball 40, anda line segment Z which is tangent to both the associated lower ball 40and the upper-rail lower-ball contact R-portion 34, at an angle in therange from 80 degrees to less than 90 degrees, more desirably in therange from 80 to 88 degrees. By setting the outward crossing angle α inthis manner, the pair of upper-rail side walls 32 can be securely madeto be resiliently deformable inwardly (i.e., in directions toward eachother) via the lower balls 40, Conversely, deformation of the pair ofupper-rail side walls 32 outwardly in opposite directions away from eachother may deteriorate the slidability of the slide rail device 10.

In other words, the load carrying capacity of the upper rail 30 becomesmaximum in theory when the line segment Y and the line segment Zintersect each other at right angles (at an angle of 90 degrees).However, if the upper rail 30 is designed so that the line segment Y andthe line segment Z intersect each other at right, angles, the outwardcrossing angle may become greater than 90 degrees when the shape of theupper rail 30 varies due to manufacturing error, and consequently, thepair of upper-rail side walls 32 become easy to deform outwardly, thushaving an adverse effect on the slidability of the slide rail device 10.In the present embodiment of the slide rail device 10, the shape of theslide rail device 10 is defined so that the outward crossing angle isalways less than 90 degrees even with the presence of manufacturingerror. This definition of the shape of the upper rail 30 in its freestate is independent from the aforementioned features of the radius ofcurvature R1 of the lower-rail lower-ball contact R-portions and theradius of curvature R1′ of the upper-rail lower-ball contact R-portions34 (being each defined greater than the radius r1 of the lower balls 40)and of the radius of curvature R2 of the lower-rail upper-ball contactR-portions 26 and the radius of curvature R2′ of the upper-railupper-ball contact R-portions 35 (being each defined greater than theradius r2 of the upper balls 50).

Obvious changes may be made in the specific embodiment of the presentinvention described herein, such modifications

being within the spirit and. scope of the invention claimed. It isindicated that all matter contained herein is illustrative said does notlimit the scope of the present invention.

1. A slide rail device which includes a lower rail having a uniformcross section, an upper rail having a uniform cross section which isfreely slidably engaged with said lower rail, and balls which areinstalled between said lower rail and said upper rail, wherein saidlower rail comprises: a lower-rail bottom wall; a pair of lower-railside walls which extend upward from both ends of said lower-rail bottomwall, with respect to a lateral direction, respectively; a pair oflower-rail upper walls which extend toward a center of said lower railin the lateral direction from upper ends of said pair of lower-rail,side walls, respectively; and a pair of lower-rail lower-ball contactR-portions via which said pair of lower-rail side walls are connected tosaid lower-rail bottom wall, respectively; and a pair of lower-railupper-ball contact R-portions via which said pair of lower-rail upperwalls are connected to said pair of lower-rail side walls, respectively,wherein said upper rail comprises: an upper-rail top wall; a pair ofupper-rail side walls which are continuous with said upper-rail top walland extend downward between said pair of lower-rail upper walls intosaid lower rail from both sides of said upper-rail top wall with respectto said lateral direction, respectively; and a pair of upper-railball-bearing walls winch extend outwardly upwards from lower ends ofsaid pair of upper-rail side walls, respectively, wherein each of saidpair of upper-rail ball-bearing walls includes an upper-rail lower-ballcontact portion which is formed to face an adjacent lower-raillower-ball contact R-portion of said pair of lower-rail lower-ballcontact R-portions of said lower rail wherein said balls include a pairof lower balls which are installed between said pair of lower-raillower-ball contact R-portions of said lower rail and said upper-raillower-ball contact portions of said pair of upper-rail ball-bearingwalls of said upper rail, respectively, and wherein a radius ofcurvature of said lower-rail lower-ball contact R-portion of said lowerrail is greater than a radius of said lower ball. 2-3. (canceled)
 4. Theslide rail device according to claim 2, wherein said upper-raillower-ball contact portion of each of said pair of upper-railball-bearing walls of said upper rail is formed as an upper-raillower-ball contact R-portion that is formed into a circular arc shapewith a specific curvature in cross section, a radius of curvature ofsaid upper-rail lower-ball contact R-portion being greater than saidradius of said lower ball.
 5. The slide rail device according to claim1, wherein the following conditions are satisfied:R1≧1.1r1, and wherein r1 designates said radius of said lower ball, andR1 designates said radius of curvature of said lower-rail lower-ballcontact R-portion
 6. (canceled)
 7. The slide rail device according toclaim 1, wherein said lower rail further comprises a pair of lower-railinner side walls which are positioned between said pair of lower-railside walls and extend downward from inner ends of said pair oflower-rail upper walls, respectively.
 8. (canceled)